Fluid mixers are well known for example in the field of exhaust systems of motor vehicles. To enable a catalytic reaction of exhaust gas in a catalytic converter, a reducing agent, typically ammonia or urea, is mixed with the exhaust gas. For example in US 2002116916, upstream of a catalytic converter, grids are arranged next to an injection device for injecting the reducing agent. The grids provide an even distribution of the exhaust gas/reducing agent mixture. While fluid mixers and catalytic converters in exhaust systems are primarily used to remove noxious components, such as nitrogen oxides from the exhaust gas, catalytic reactions of exhaust gases may also be used to use up remaining fuel left in the exhaust gas. If reaction heat produced in this process is used, energy efficiency of a system may be enhanced.
Fuel cells are known as energy converters with high efficiency. In fuel cells, for example hydrocarbon fuels are directly converted into electrical energy and heat. In order to enhance an overall efficiency of an energy system the heat produced in the fuel cell may further be used for heating. Especially fuel cells operating at high temperatures, such as solid oxide fuel cells (SOFC), are suitable candidates for application in combined power generation and heat recovery devices. In general, a heat exchanger is arranged downstream of the fuel cell heating up a cool fluid for further use. For operation, SOFCs need a preheated oxidizing gas, especially air. This gas may be preheated in the heat exchanger before it is introduced into the SOFC. Furthermore, if a fuel introduced into the fuel cell is not completely used up such a depleted fuel leaving the fuel cell still contains fuel. The depleted fuel may now be mixed in a fluid mixer with the hot air leaving the SOFC for oxidizing the depleted fuel/hot air mixture. The mixture is then guided into the heat exchanger. The heat from the hot air as well as the reaction heat from the oxidizing reaction is used in the heat exchanger. Unfortunately, such systems include several individual components that require space and have high production costs, for example a separate fluid mixer and a separate heat exchanger. Another example consists of a separate burner and a separate heat exchanger, whereas the depleted fuel is mixed and oxidized in the said separate burner, which is placed upstream of the separate heat exchanger.